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Hydroxides and oxides of iron-based elements
Fe(OH) 2 is white, and it reacts with oxygen in the air to quickly turn into gray-blue-green.
After all is oxidized, it produces brown Fe(OH) 3 , and Fe(OH) 3 is dehydrated to produce reddish brown Fe 2 O 3 (called iron red ).
Or iron red)
.
Fe 2 O 3 can be used as a red pigment (such as in red paint) and polishing powder, and a-Fe 2 O 3 can be used as a magnetic material for audio tapes
FeO black powder, CoO gray green, NiO dark green, Fe 2 O 4 black
.
Fe 3 O 4 has strong ferromagnetism and good conductivity (the result of electron transfer between Fe 2+ and Fe 3+ )
Adding the NaOH solution to the Co 2+ solution first produces a blue precipitate, which is converted into pink when placed or heated, namely Co(OH) 2.
There are two variants
.
Co(OH) 2 is slowly oxidized in the air to brown-black Co(OH) 3 (or written as Co 2 O 3 ·nH 2 O)
Adding the NaOH solution to the Ni 2+ solution produces a light green Ni(OH) 2 precipitate, which does not change in the air
.
With strong oxidants, Ni(OH) 2 can be oxidized to NiO(OH) (brown-black, some people think it is NiO 2 )
Important iron salt
The anhydrous iron halides include: FeF 2 , FeCl 2 , FeBr 2 , Fel 2 , FeF 3 , FeCl 3 , FeBr 3
.
As the oxidation number of iron increases and the radius of the halogen increases, the color of the halide becomes darker
Adding NaF solution to FeCl 3 solution generates white FeF 3 precipitate (the color does not change when dried at 100~120℃), and FeF 3 is dissolved in excess F-solution (generates more stable complex ion [FeF 5 ] 2- )
.
FeCl 3 is an important chemical raw material and can be used as an etching agent for printed circuit boards and a flocculant for water treatment
.
FeCl 3 has obvious covalent components and is easily soluble in ethanol ; FeCl 3 turns into covalent compounds at high temperatures (dimers in the gaseous state, Figure 16-5)
Anhydrous FeSO 4 white powder, FeSO 4 ·7H 2 O is green, commonly known as green alum; FeSO 2 ·(NH 4 ) 2 SO 4 ·6H 2 O light blue-green, Mohr salt; Fe(SCN) 2 ·3H 2 O green
.
FeCl 3 ·6H 2 O orange, Fe(NO 3 ) 3 ·9H 2 O and Fe(NO 3 ) 3 ·6H 2 O lavender (same color as hydrate ions), NH 4 Fe(SO 4 ) 2 ·12H 2 O liquid purple (called iron press), Fe(SO 4 ) 3 ·9H 2 O yellow
.
Fe 2 (SO 4 ) 3 is white, Fe(SCN) 3 is purple-red
Figure 16-5 FC13 dimer knot
Important cobalt and nickel salts
The anhydrous salt of cobalt is CoF 2 red, CoCl 2 blue, CoBr 2 green, Col 2 blue-black, Co(NO 3 ) 2 lavender, CoSO 4 red, and Co(SCN) 2 brown-yellow
.
The anhydrous nickel salt NiF 2 is yellow, NiCl 2 is yellow, NiBr 2 is yellow, Nil 2 is black, Ni(NO 3 ) 2 is green, NiSO 4 is yellow-green, and Ni(SCN) 2 is green
.
Among the hydrated salts of cobalt, the hexahydrate salt is pink or red (the color of hydrated ions), such as CoCl 2 ·6H 2 O, CoBr 2 ·6H 2 O, Col 2 ·6H 2 O, CoSO 4 ·7H 2 O , Co(NO 3 ) 2 ·6H 2 O; With the decrease of crystal water, the color is between hydrated ions and anhydrous salts, such as CoCl 2 ·H 2 O blue-purple, CoC 2 ·2H 2 O purple-red, Col 2 ·2H 2 O is green, and Col 2 ·4H 2 O is green
.
Co(SCN) 2 ·4H 2 O is red
Ni 2+ compound and a hydrated salt crystal mostly green, such as NiCl 2 · 6H 2 O, Nil 2 · 6H 2 O, NiSO .
Related Links: Solubility and Hydrolysis of Iron Compounds